Interpretive Summary: As many as 5 percent of school-age children have attention-deficit/ hyperactivity disorder (AD/HD), generally characterized by inattention, impulsiveness, and overactivity. Such children are often prescribed stimulant medications like methylphenidate, which usually modifies these traits. We used a room respiration calorimeter and motion detectors to determine how stimulant medications affected energy expenditure and physical activity in 31 children with AD/HD, both on and off their medication. The medications decreased their energy expenditure and physical activity. Based on the results, we conclude that stimulant medications decrease physical activity and thus, decrease the activity component of energy expenditure in children with this disorder.

Technical Abstract:
Objective: To determine the effect of stimulant medications on energy expenditure, fuel utilization and physical activity in children with attention-deficit/hyperactivity disorder (AD/HD). Study design: Energy expenditure, fuel utilization and physical activity were measured by room respiration calorimetry and microwave motion detectors in 31 children with AD/HD (26 boys, 5 girls; ages 6 to 12 y) once after they had been off medication for at least 24 h and once while the children were receiving their prescribed stimulant medication. Results: Total and awake energy expenditure were 4-5% and 6-7% lower, respectively, while the children were receiving their prescribed stimulant medication. Total and awake activity counts were 16-22% lower while on medication, and accounted for the lower rates of energy expenditure. Energy expended while doing schoolwork, riding a stationary bicycle, resting, and watching a movie was lower in each case while on medication. Sleeping metabolic rate, basal metabolic rate and fue utilization were unaffected by drug therapy. Conclusions: Stimulant medications decrease physical activity and, hence, decrease the activity component of total daily energy expenditure in children with AD/HD.